The effect of biological substrates on the ultrafast excited-state dynamics of zinc phthalocyanine tetrasulfonate in solution.
Zinc phthalocyanine tetrasulfonate (ZnPcS4), a potential photosensitizer for photodynamic therapy (PDT), has been studied using femtosecond laser spectroscopy. The excited-state dynamics in water have been found to be fast (< 80 ps) and dominated by intermolecular aggregation. Since the proposed mechanism for PDT is energy transfer from the triplet excited state of the photosensitizer to triplet O2 creating singlet O2, the short lifetime is expected to be unfavorable for producing singlet O2. This leads to the suggestion that the presence of biological substrates may have an effect on the excited-state dynamics. To test this hypothesis, the lifetimes of the excited states of ZnPcS4 have been directly measured in the presence of a model membrane, n-hexadecyltrimethylammonium bromide (CTAB). The excited-state dynamics of ZnPcS4 in buffer solutions and with human serum albumin (HSA) have also been measured. The presence of HSA and CTAB increases the excited-state lifetime significantly relative to that observed in water. The longer lifetime of ZnPcS4 in CTAB (> 1 ns) indicates that the micellar surface favors monomer formation. By increasing the excited-state lifetime, the surface substantially increases the photosensitizing potential of ZnPcS4.
Howe
L
L
Department of Chemistry and Biochemistry, University of California, Santa Cruz 95064, USA.
Zhang
J Z
JZ
D001798:Blood Proteins; D000077286:Cetrimonium; D002593:Cetrimonium Compounds; D003902:Detergents; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007211:Indoles / Q000737:chemistry*; D007834:Lasers; D009942:Organometallic Compounds / Q000737:chemistry*; D010778:Photochemotherapy; D011838:Radiation-Sensitizing Agents / Q000737:chemistry*; D012709:Serum Albumin; D012996:Solutions; D013054:Spectrophotometry, Atomic; D015032:Zinc
D001798:Blood Proteins; D002593:Cetrimonium Compounds; D003902:Detergents; D007211:Indoles; D009942:Organometallic Compounds; D011838:Radiation-Sensitizing Agents; D012709:Serum Albumin; D012996:Solutions; C052735:zinc tetrasulfophthalocyanine; D015032:Zinc; D000077286:Cetrimonium